This invention relates to improvements in aircraft flight safety control systems and more specifically to a minimum safe altitude display and warning system which automatically signals to the pilot on an ongoing basis existing or imminent flight altitude requirements in order to avoid hazard situations. The invention which may be applied to submarines, as well as airplanes, for example, is herein illustratively described by reference to its presently preferred forms as applied to aircraft and as used in conjunction with currently available navigational computer technology and related instrumentation. However, it will be recognized that certain modifications and changes therein with respect to details may be made and that the invention may be embodied in a variety of forms without departing from the essential features involved.
A survey of prior art proposals potentially of interest as background to this invention, revealed the following prior art U.S. Pat. Nos.: 2,568,568, 3,113,306, 2,585,605, 3,231,887, 2,606,317, 3,246,326, 2,809,340, 3,328,795, 3,060,426, 3,705,306, 2,582,588, 3,805,261, 3,680,046.
Of the foregoing patents, the following are believed to be representative of the group in providing an indication of the state of the background art of interest herein.
U.S. Pat. No. 3,113,306 discloses a fuel saving system involving a precalculated trip altitude and vertical speed profile with deviation monitoring to make appropriate enroute corrections in flight so as to permit the aircraft to fly over a selected destination point at preselected altitude.
U.S. Pat. No. 3,328,795 discloses a fix-taking or place-finding guidance system using quantized topographic elevation data taken as a sequence of discrete elevation readings at selected points during vehicle travel. Position is determined for navigational purposes by comparison matching of these sequential altitude values with prerecorded sequences also in quantized form in the computer memory bank. Present position is determined on the basis of "best fit" of the sequence patterns being compared. U.S. Pat. No. 3,805,261 is generally of a similar nature.
U.S. Pat. No. 3,582,588 discloses a navigational system with a moving recording medium representing aircraft motion associated with means indicating altitude clearance and a means indicating oncoming elevation hazards of which the pilot should be made aware in order to take appropriate avoidance measures.
In U.S. Pat. No. 3,680,046 an assigned or command altitude corridor is set by the crew using thumbwheel switches converting the altitude corridor into digital form which is compared with a digital representation of existing altitude using BCD logic to produce altitude deviation warnings.
A broad object of this invention is to provide an improved minimum safe altitude indication and/or warning system that substantially avoids all necessity associated with prior practices of relying upon the pilot's observations, judgments and responses relative to ground hazards when attempting to reduce altitude safely and to follow a safe course at low relative altitude. A related object is to remove the added strain and associated responsibility with attendant risk of human error placed upon the pilot under those conditions regardless of whether or not radar guidance or other hazard detection or course directing equipment or personnel are available to assit. The risk, of course, becomes extreme under poor visibility conditions, and yet, sometimes that risk is taken because of operational mistakes or imperative demands to reduce altitude in making final approaches.
In accordance with the present invention, by continuously indicating to the pilot what is the minimum safe altitude and/or warning the pilot of imminent descent below minimum safe altitude and by basing the determinations thereof on data that is as reliable as the navigation computer itself and other basic instrumentation, which data already incorporates or is based upon "worst case" conditions, the necessity of maintaining a collision "watch" and exercising low altitude hazard avoidance judgments is minimized and the pilot can direct his principal focus of attention upon other vital tasks.
In effect, the invention provides to the pilot ongoing information that assures keeping the aircraft out of trouble from the standpoint of ground hazards, while permitting the aircraft to be flown as low as safely permissible within that specification. A related object hereof is to provide an ongoing monitor and indication of minimum safe altitude that combines the reliability of geographically based prerecorded present position altitude data and projected position altitude data with the reliability of navigation computer coordinate derivations.
A more specific object hereof is to provide a system which may be implemented in a non-tactical or universally applicable form or alternatively in a tactical form in which the prerecorded minimum safe altitude data is utilized in conjunction with such variable factors as ground speed and ground track as well as altitude change rate in order to provide a higher degree of resolution in interpreting the prerecorded data allowing the aircraft to fly safely at even lower indicated minimum safe altitudes. In either design approach, the prerecorded minimum safe altitude data is based on actual terrain features precisely located in terms of geographic coordinates and related to other terrain features similarly determined for location. These are accounted for in the anticipatory or course projection determinations necessary to assure that an aircraft in any given position can be safe only if above a certain minimum altitude. Thus the determinations allow for terrain features immediately ahead in whatever direction and at whatever velocity the aircraft may be proceeding.
These and other objects and advantages of the invention will become more fully evident from the description that follows